1. Field of the Invention
The present invention relates to a thin-film device having an electrically conductive thin-film, such as a coil layer, and an electrical conductor, such as a lead layer and a bump, which are in contact with the surface of the electrically conductive thin-film, and more particularly, relates to a thin-film device in which contact failures can be reduced and stability of direct current resistance can be improved by improving cohesion and electrical conduction between the electrically conductive thin-film and the electrical conductor, and relates to a manufacturing method therefor.
2. Description of the Related Art
FIG. 10 is a cross-sectional view of a conventional magnetoresistive (MR)/inductive hybrid head. In a reading MR thin-film magnetic head h1 of the MR/inductive hybrid head, an alumina undercoat film 1a is formed on a slider 1 composed of alumina-titanium-carbide, and a laminated structure, which is composed of a lower shield layer 2, a lower gap layer 3, an MR element layer 4, an electrode layer 5, an upper gap layer 6, and an upper shield layer 7, is formed on the alumina undercoat layer 1a. 
A recording inductive head h2 provided on the reading MR thin-film magnetic head h1 is a laminated structure composed of a lower core layer 7 which is also used as the upper shield layer 7, a gap layer 8a, an insulating layer 8b, a coil layer 9, an insulating layer 10, an upper core layer 11, a lead layer 12, and an insulating layer 13. A front end of the gap layer 8a, which is disposed between the lower core layer 7 and the upper core layer 11 and opposes a recording medium, forms a magnetic gap G.
The lead layer 12 is in contact with an electrode for an external connection composed of a bump 15 and a bonding pad 16 at the other edge of the lead layer 12, which is opposite to the edge thereof in electrical contact with a central edge 9a of the coil layer 9, via an elevating layer 14 made of the same material as was used for the coil layer 9.
FIG. 11 is an enlarged partial cross-sectional view of a contact area between the coil layer 9 and the lead layer 12 of the inductive head h2 for recording data on a magnetic recording medium.
The coil layer 9 as an electrically conductive thin-film is composed of a copper layer 9c as an electrically conductive material layer formed by flame plating above the insulating layer 8b, which is provided on the gap layer 8a of the inductive head h2, via a coil base layer 9b composed of titanium and copper. The coil layer 9 is flatly coiled on the insulating layer 8b. The lead layer 12, which is an electrical conductor, is formed above the coil layer 9 via the insulating layer 10. The lead layer 12 is formed by plating using permalloy. The coil layer 9 and the lead layer 12 are in electrical contact with each other at the central edge 9a of the coil layer 9.
FIGS. 12 to 17 are cross-sectional views of the inductive head h2 of the MR/inductive hybrid thin-film magnetic head shown in FIG. 10 in a manufacturing process therefor.
FIG. 12 shows a state of the insulating layer 8b composed of a hard-baked resist formed on the gap layer 8a composed of Al2O3, SiO2, or the like provided on the lower core layer 7.
FIG. 13 shows a state of the coil base layer 9b in a laminated structure composed of titanium and copper formed on the insulating layer 8b by a vacuum film deposition process, such as sputtering, and the copper layer 9c of the electrically conductive material layer formed on the coil base layer 9b by flame plating. The copper layer 9c is flatly formed in the form of a coil on the coil base layer 9b. 
In addition, the coil base layer 9b exposed by the copper layer 9c is removed by dry-etching such as by ion-milling using argon ions, and as a result, the coil layer 9 composed of the coil base layer 9b and the copper layer 9c is formed as shown in FIG. 14.
Next, as shown in FIG. 15, the insulating layer 10 is formed on the coil layer 9. In this step, an opening 10a is formed in the insulating layer 10 at the position at which the central edge 9a of the coil layer 9 is present.
As shown in FIG. 16, a plating base layer 17 (not shown in FIGS. 10 and 11) to form the upper core layer 11 and the lead layer 12 by plating is formed on the insulating layer 10 by sputtering. The plating base layer 17 is made of, similarly to the upper core layer 11 and the lead layer 12, permalloy or the like. In this step, the surface of the central edge 9a of the coil layer 9 in the opening 10a is covered with the plating base layer 17.
In addition, the upper core layer 11 and the lead layer 12 are simultaneously formed on the plating base layer 17 by plating using permalloy, and the surfaces of the upper core layer 11 and the lead layer 12 are covered with the insulating layer 13. A front end of the gap layer 8a, which is disposed between the lower core layer 7 and the upper core layer 11 and opposes a recording medium, forms the magnetic gap G. FIG. 17 is a cross-sectional view of the completed inductive head h2 in a laminated structure.
In the conventional inductive head h2 described above, in the step for removing the coil base layer 9b exposed by the copper layer 9c, as shown in FIG. 13, by ion-milling or the like, the upper surface of the copper layer 9c is polished, as is the coil base layer 9b. When the upper surface of the copper layer 9c is polished, direct current resistance of the coil layer 9 varies, and hence, there is a problem in that product characteristics of the manufactured inductive head h2 are degraded. In addition, when ion-milling is performed, bombardment by argon ions on the upper surface of the copper layer 9c may cause damage, such as residual stress in the copper layer 9c, and hence, there is also a problem in that direct current resistance of the coil layer 9 varies.
Furthermore, between the formations of the coil layer 9 and the insulating layer 10, the coil layer 9 is exposed to the air in some cases as shown in FIG. 14. In addition, the central edge 9a of the coil layer 9 is exposed in the opening 10a in the insulating layer 10 in the state of the insulating layer 10 formed as shown in FIG. 15, and accordingly, the central edge 9a of the coil layer 9 may be exposed to the air until the plating base layer 17 is formed so as to cover the upper surface of the central edge 9a in the opening 10a of the insulating layer 10.
When the coil layer 9 is exposed to the air, the surface of the coil layer 9, which is an electrically conductive thin-film, is oxidized, and the oxide layer forms. In particular, when the insulating layer 10 is heat-cured to planarize the surface thereof, the central edge 9a of the coil layer 9 in the opening 10a is exposed to the air, and hence, is susceptible to forced oxidation.
In the case in which the surface of the coil layer 9 is oxidized, i.e., in which the oxide layer forms thereon, cohesion between the coil layer 9 and the insulating layer 10 formed thereon, and between the coil layer and the lead layer 12 are degraded, and separation thereof readily occur. In particular, in the case in which the central edge 9a of the coil layer 9, which is in contact with the lead layer 12, is oxidized, degradation in electrical conduction as well as the degradation in the cohesion with the lead layer 12 occurs. Consequently, the direct current resistance of the inductive head h2 becomes unstable and recording characteristics thereof are degraded.
When the oxide layer forms on the coil layer 9, there are methods for removing the oxide layer by dry etching, such as by ion-milling. However, the thickness of the oxide layer formed on the surface of the coil layer 9, that is, the copper layer 9c, varies in accordance with the conditions when the oxide layer forms, and the thickness of the oxide layer formed on the coil layer 9 cannot be predicted.
Consequently, when the conditions for ion-milling are determined so as to remove a predetermined thickness of the oxide layer formed on the coil layer 9, products having remaining oxide layer may be manufactured, or conversely, an area of the coil layer 9, which is not oxidized, may be removed. Accordingly, there is a problem in that characteristics of the thin-film structures vary from product to product. It is not practical to vary the conditions for ion-milling in accordance with the respective measured thickness of the oxide layer formed on the coil layer 9 during manufacturing.
Degradation in cohesion between an electrically conductive thin-film and an insulating layer formed thereon, and degradations in cohesion and electrical conduction between the electrically conductive thin-film and an electrical conductor in contact therewith, caused by oxidation of the electrically conductive thin-film, such as a coil layer, in manufacturing steps, are problems not only in the thin-film magnetic heads, but also in thin-film inductors, thin-film transistors, and general thin-film devices.
In order to solve the conventional problems described above, it is an object of the present invention to provide a thin-film device and a manufacturing method therefor, in which an oxide layer formed on an electrically conductive thin-film, such as a coil layer of a thin-film device, can be reliably removed, and cohesion and electrical conduction between the electrically conductive thin-film and an electrical conductor in contact therewith can be improved. Consequently, connection failures in the thin-film device can be reduced, and stability of direct current resistance thereof can be improved.
A thin-film device of the present invention comprises an electrically conductive thin-film and an electrical conductor in contact therewith, in which the electrically conductive thin-film has an electrically conductive material layer and an electrically conductive protective layer having a predetermined thickness formed on the electrically conductive material layer.
The electrically conductive thin-film forming a coil layer and the like of the thin-film device of the present invention has a structure provided with the electrically conductive material layer protected by the electrically conductive protective layer. Consequently, in a step of removing an unwanted coil base layer by dry etching, such as by ion-milling, when the coil layer is formed, removal of the upper surface of the electrically conductive material layer in addition to that of the coil base layer can be avoided.
Accordingly, change in the volume of the electrically conductive material layer can be prevented. Since the volume of the electrically conductive material layer is a parameter determining allowable current and direct current resistance of the electrically conductive thin-film, and since a change in the volume of the electrically conductive material layer can be prevented, a thin-film device can be easily provided with the electrically conductive thin-film having uniform allowable current and direct current resistance, and uniform characteristics in the thin-film device be easily obtained.
In addition, when ion-milling is performed, bombardment by argon ions on the upper surface of the electrically conductive material layer can be prevented, and hence, damage such as residual stress in the upper surface of the electrically conductive material layer can be avoided. Accordingly, in the present invention, the thin-film device having uniform direct current resistance can be obtained.
The electrically conductive protective layer preferably comprises a material, in which an oxide layer formed on the material grows to a thickness of not more than that of the electrically conductive protective layer. The electrical conductor is preferably in contact with an area at which the oxide layer on the electrically conductive protective layer is removed therefrom.
When the electrically conductive protective layer comprises the material described above, the oxide layer formed on the material at room temperature or an elevated temperature grows to a thickness of not more than the electrically conductive protective layer. Consequently, even though the oxide layer is formed on the electrically conductive protective layer, when not less than the maximum thickness of the oxide layer grown on the surface of the electrically conductive protective layer is polished away therefrom by dry etching, such as by ion-milling, the oxide layer can be reliably removed.
In the thin-film device of the present invention, since the electrical conductor, such as a lead layer or the like, is in contact with the area at which the oxide layer on the electrically conductive protective layer is removed, the cohesion and electrical conduction between the electrically conductive thin-film and the electrical conductor can be improved. Accordingly, connection failures of the thin-film device can be reduced. In addition, the direct current resistance of the thin-film device can be stabilized, and the characteristic thereof can be improved.
When the electrically conductive protective layer having a predetermined thickness of the thin-film device of the present invention comprises the material, in which the oxide layer formed thereon at room temperature or an elevated temperature grows to a thickness of not more than that of the electrically conductive protective layer, the oxide layer on the surface of the electrically conductive protective layer can be removed by ion-milling or the like so as to only polish the electrically conductive protective layer without polishing the electrically conductive material layer. Consequently, a change in the volume of the electrically conductive material layer is prevented, and hence, a thin-film device provided with the electrically conductive thin-film having uniform allowable current and direct current resistance can be formed.
The electrically conductive material layer and the electrically conductive protective layer must be formed at sufficient thicknesses so as to increase allowable current and so as to decrease direct current resistance. Hence, the electrically conductive material layer and the electrically conductive protective layer are preferably formed by plating.
The electrically conductive material layer is preferably an electrically conductive non-magnetic layer comprising at least one layer containing at least one element selected from copper and silver. The electrically conductive protective layer is preferably an electrically conductive non-magnetic layer comprising at least one layer containing at least one element selected from the group consisting of nickel, phosphorus, palladium, platinum, boron, and tungsten.
It has been experimentally confirmed that the oxide layer formed on the materials mentioned above used for the electrically conductive protective layer does not exceed a certain thickness at room temperature or an elevated temperature.
For example, when the electrically conductive protective layer is a nickel layer, and when an oxide layer forms on the electrically conductive protective layer, it has been experimentally confirmed that the oxide layer does not exceed approximately 3.0 nm from the surface of the electrically conductive protective layer. As a result, by polishing away not less than 3.0 nm of the electrically conductive protective layer from the surface thereof by dry etching, such as by ion-milling, the oxide layer can be reliably removed.
In addition, allowable current and direct current resistance of the electrically conductive thin-film are also determined by a material used for the electrically conductive material layer. In the case in which the electrically conductive material layer is an electrically conductive non-magnetic layer comprising at least one layer containing at least one element selected from copper and silver, an electrically conductive thin-film having low direct current resistance and high allowable current can be formed.
When a coil layer for a thin-film device or the like is formed by using the electrically conductive thin-film of the present invention, and when an electrically conductive material layer and an electrically conductive protective layer, which form the electrically conductive thin-film, are made of the electrically conductive non-magnetic material, such as nickel or copper, an influence to impedance of the coil layer can be prevented.
When the electrically conductive material layer is an electrically conductive non-magnetic layer comprising at least one layer containing at least one element selected from copper and silver, and the electrically conductive protective layer is an electrically conductive non-magnetic layer comprising at least one layer containing at least one element selected from the group consisting of nickel, phosphorus, palladium, platinum, boron, and tungsten, stress can be reduced when the electrically conductive thin-film is formed by providing the electrically conductive protective layer on the surface of the electrically conductive material layer. As a result, the electrically conductive material layer and the electrically conductive protective layer are difficult to separate from each other.
The electrically conductive protective layer may be formed on the entire surface of the electrically conductive material layer, and accordingly, the entire surface of the electrically conductive material layer can be protected.
However, in the case in which an insulating layer having an opening covering the electrically conductive thin-film is provided, the electrically conductive protective layer may be formed on the electrically conductive material layer only at an area thereof exposed in the opening provided in the insulating layer.
Since the electrical conductor is in contact with the surface of the electrically conductive thin-film only at the area thereof exposed in the opening in the insulating layer, even when the oxide layer present only in the opening of the insulating layer is reliably removed, the cohesion and electrical conduction between the electrically conductive thin-film and the electrical conductor can be improved, and the direct current resistance of the thin-film device can be stabilized.
In the thin-film device of the present invention, for example, the electrically conductive thin-film is a coil layer and/or a lead portion integrally extending from the coil layer in a thin-film magnetic head comprising a core layer to form a gap at an area thereof opposing a recording medium and the coil layer flatly coiled to induce a recording magnetic field to the core layer, and the electrical conductor is in contact with the coil layer and/or the lead layer.
A method for manufacturing a thin-film device of the present invention comprises a step (a) of forming an electrically conductive material layer by plating, a step (b) of forming an electrically conductive protective layer having a predetermined thickness by plating using a material on the electrically conductive material layer, in which an oxide layer formed on the material grows to a thickness of not more than a predetermined thickness at room temperature or an elevated temperature, a step (c) of removing the oxide layer on the surface of the electrically conductive protective layer; and a step (d) of forming an electrical conductor on the surface of the electrically conductive protective layer at which the oxide layer is removed.
According to the method for manufacturing the thin-film device of the present invention, the electrically conductive protective layer having a predetermined thickness is formed by using the material, in which the oxide layer on the surface of the material grows to a thickness of not more than a predetermined thickness at room temperature or an elevated temperature. Consequently, even though the oxide layer forms on the surface of the electrically conductive protective layer following the step (b), the oxide layer can be reliably removed by polishing away not less than the maximum thickness of the oxide layer grown from the surface of the electrically conductive protective layer by dry etching, such as by ion-milling with argon ions in the step (c).
Furthermore, in the step (d), the electrical conductor, such as a lead layer, is formed on the surface of the electrically conductive protective layer at an area thereof at which the oxide layer is removed, and hence, the cohesion and electrical conduction between the electrically conductive thin-film composed of the electrically conductive material layer and the electrically conductive protective layer and the electrical conductor can be improved. Accordingly, connection failures of the thin-film device can be reduced. In addition, the direct current resistance of the thin-film device can be stabilized, and the characteristics thereof can be improved.
In the method for manufacturing the thin-film device of the present invention, since the electrically conductive protective layer having a predetermined thickness is formed using the material in the step (b), in which the oxide layer formed on the surface of the material grows to a thickness of not more than a predetermined thickness, the oxide layer on the surface of the electrically conductive protection layer can be removed by ion-milling or the like in the step (c) so as to only polish away the electrically conductive protective layer without polishing the electrically conductive material layer. Consequently, since change in the volume of the electrically conductive material layer can be prevented, a thin-film device having the electrically conductive thin-film provided with uniform allowable current and direct current resistance can be formed, and uniform characteristics of the thin-film device can be easily obtained.
In addition, since bombardment ions, such as argon ions, used for ion-milling only collide with the electrically conductive protective layer and do not collide with the upper surface of the electrically conductive material layer, damage, such as residual stress, on the surface of the electrically conductive material layer can be avoided. As a result, an advantage of direct current resistance stabilization of the electrically conductive thin-film can be obtained.
The electrically conductive material layer is preferably formed in at least one layer composed of a material containing at least one element selected from copper and silver, and the electrically conductive protective layer is preferably formed in at least one layer composed of a material containing at least one element selected from the group consisting of nickel, phosphorus, palladium, platinum, boron, and tungsten.
When the electrically conductive material layer is formed in at least one layer by the material mentioned above, even though the oxide layer forms on the electrically conductive protective layer, it has been experimentally confirmed that the thickness of the oxide layer from the surface of the electrically conductive protective layer grows to a thickness of not more than a certain thickness.
For example, when the electrically conductive protective layer is a nickel layer, it is understood that the thickness of an oxide layer formed on the electrically conductive protective layer from the surface thereof will not exceed 3.0 nm. Consequently, by polishing away 3.0 nm or more of the electrically conductive protective layer from the surface thereof by ion-milling in the step (c), the oxide layer can be reliably removed.
In addition, allowable current and direct current resistance of the electrically conductive thin-film are also determined by a material used for the electrically conductive material layer. In the case in which the electrically conductive material layer is formed in at least one layer composed of a material containing at least one element selected from copper and silver, an electrically conductive thin-film having low direct current resistance and high allowable current can be formed.
In the case in which a coil layer for a thin-film device or the like is formed by using the electrically conductive thin-film of the present invention, when an electrically conductive material layer and an electrically conductive protective layer, which form the electrically conductive thin-film, are made of the electrically conductive non-magnetic material, such as nickel or copper, an influence to impedance of the coil layer can be prevented.
When the electrically conductive material layer is formed of an electrically conductive non-magnetic layer comprising at least one layer containing at least one element selected from copper and silver, and when the electrically conductive protective layer is formed of an electrically conductive non-magnetic layer containing at least one element selected from the group consisting of nickel, phosphorus, palladium, platinum, boron, and tungsten, stress can be reduced when the electrically conductive thin-film is formed by providing the electrically conductive protective layer on the surface of the electrically conductive material layer. As a result, the electrically conductive material layer and the electrically conductive protective layer are difficult to separate from each other.
When a plurality of removing steps of removing an oxide layer is performed in the step (c), the electrically conductive protective layer is preferably formed in the step (b) so as to have a thickness of not less than the total thickness to be removed in the plurality of removing steps.
When the present invention is practiced, the removing step of removing the oxide layer by ion-milling is not necessarily performed once.
For example, when the coil layer of the inductive head is formed, a removing step is performed to remove an oxide layer formed on a coil layer at the same time to remove an unwanted coil base layer, and in addition, when an opening is formed, which is formed in an insulating layer formed on the coil layer and is used as a contact area between the coil layer and a lead layer, another removing step of removing an oxide layer formed on the surface of the coil layer exposed to the air in the opening may be performed. In the case as described above, in order to prevent the electrically conductive material layer beneath the electrically conductive protective layer from being polished, the electrically conductive protective layer is preferably formed to a thickness of not less than the total thickness to be removed by performing ion-milling twice.
In the method for manufacturing the thin-film device of the present invention, for example, when a thin-film magnetic head having a core layer to form a gap at an area thereof opposing a recording medium and a coil layer flatly coiled so as to induce a recording magnetic field to the core layer is formed, the coil layer and/or the coil layer having a lead portion integrally extending therefrom is formed in the step (a) and the step (b), and a lead layer and/or a bump, which is different from the coil layer, is formed as the electrical conductor by plating in the step (d).